Editing Cyanobacteria (section)

=== Origin of chloroplasts ===
{{See also|Chloroplast#Chloroplast lineages and evolution}}

Primary chloroplasts are cell organelles found in some [[eukaryote|eukaryotic]] lineages, where they are specialized in performing photosynthesis. They are considered to have evolved from [[endosymbiotic]] cyanobacteria.<ref name="ReferenceA">{{cite journal | vauthors = Keeling PJ | title = The number, speed, and impact of plastid endosymbioses in eukaryotic evolution | journal = Annual Review of Plant Biology | volume = 64 | pages = 583–607 | year = 2013 | issue = 1 | pmid = 23451781 | doi = 10.1146/annurev-arplant-050312-120144 | bibcode = 2013AnRPB..64..583K }}</ref><ref>{{cite journal | vauthors = Moore KR, Magnabosco C, Momper L, Gold DA, Bosak T, Fournier GP | title = An Expanded Ribosomal Phylogeny of Cyanobacteria Supports a Deep Placement of Plastids | journal = Frontiers in Microbiology | volume = 10 | pages = 1612 | date = 2019 | pmid = 31354692 | pmc = 6640209 | doi = 10.3389/fmicb.2019.01612 | doi-access = free }}</ref> After some years of debate,<ref>{{cite journal | vauthors = Howe CJ, Barbrook AC, Nisbet RE, Lockhart PJ, Larkum AW | title = The origin of plastids | journal = Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences | volume = 363 | issue = 1504 | pages = 2675–2685 | date = August 2008 | pmid = 18468982 | pmc = 2606771 | doi = 10.1098/rstb.2008.0050 }}</ref> it is now generally accepted that the three major groups of primary endosymbiotic eukaryotes (i.e. [[Viridiplantae|green plants]], [[Rhodophytes|red algae]] and [[glaucophyte]]s) form one large [[Monophyly|monophyletic group]] called [[Archaeplastida]], which evolved after one unique endosymbiotic event.<ref name="Rodríguez-Ezpeleta N 2005">{{cite journal | vauthors = Rodríguez-Ezpeleta N, Brinkmann H, Burey SC, Roure B, Burger G, Löffelhardt W, Bohnert HJ, Philippe H, Lang BF | display-authors = 6 | title = Monophyly of primary photosynthetic eukaryotes: green plants, red algae, and glaucophytes | journal = Current Biology | volume = 15 | issue = 14 | pages = 1325–1330 | date = July 2005 | pmid = 16051178 | doi = 10.1016/j.cub.2005.06.040 | doi-access = free | bibcode = 2005CBio...15.1325R }}</ref><ref>{{cite journal | vauthors = Adl SM, Simpson AG, Lane CE, Lukeš J, Bass D, Bowser SS, Brown MW, Burki F, Dunthorn M, Hampl V, Heiss A, Hoppenrath M, Lara E, Le Gall L, Lynn DH, McManus H, Mitchell EA, Mozley-Stanridge SE, Parfrey LW, Pawlowski J, Rueckert S, Shadwick L, Schoch CL, Smirnov A, Spiegel FW | display-authors = 6 | title = The revised classification of eukaryotes | journal = The Journal of Eukaryotic Microbiology | volume = 59 | issue = 5 | pages = 429–493 | date = September 2012 | pmid = 23020233 | pmc = 3483872 | doi = 10.1111/j.1550-7408.2012.00644.x }}</ref><ref>{{cite journal | vauthors = Price DC, Chan CX, Yoon HS, Yang EC, Qiu H, Weber AP, Schwacke R, Gross J, Blouin NA, Lane C, Reyes-Prieto A, Durnford DG, Neilson JA, Lang BF, Burger G, Steiner JM, Löffelhardt W, Meuser JE, Posewitz MC, Ball S, Arias MC, Henrissat B, Coutinho PM, Rensing SA, Symeonidi A, Doddapaneni H, Green BR, Rajah VD, Boore J, Bhattacharya D | display-authors = 6 | title = Cyanophora paradoxa genome elucidates origin of photosynthesis in algae and plants | journal = Science | volume = 335 | issue = 6070 | pages = 843–847 | date = February 2012 | pmid = 22344442 | doi = 10.1126/science.1213561 | bibcode = 2012Sci...335..843P }}</ref><ref name="Ponce-Toledo RI 2016">{{cite journal | vauthors = Ponce-Toledo RI, Deschamps P, López-García P, Zivanovic Y, Benzerara K, Moreira D | title = An Early-Branching Freshwater Cyanobacterium at the Origin of Plastids | journal = Current Biology | volume = 27 | issue = 3 | pages = 386–391 | date = February 2017 | pmid = 28132810 | pmc = 5650054 | doi = 10.1016/j.cub.2016.11.056 | bibcode = 2017CBio...27..386P }}</ref>

The [[Morphology (biology)|morphological]] similarity between chloroplasts and cyanobacteria was first reported by German botanist [[Andreas Franz Wilhelm Schimper]] in the 19th century<ref name="Schimper">{{cite journal | vauthors = Schimper AF |author-link=Andreas Franz Wilhelm Schimper |title=Über die Entwicklung der Chlorophyllkörner und Farbkörper |trans-title=About the development of the chlorophyll grains and stains |language=de |journal=Bot. Zeitung |year=1883 |volume=41 |pages=105–14, 121–31, 137–46, 153–62 |url=http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/19551 |url-status=dead |archive-url=https://web.archive.org/web/20131019121025/http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/19551 |archive-date=19 October 2013|df=dmy-all}}</ref> Chloroplasts are only found in [[plant]]s and [[algae]],<ref name="Molecular biology of the cell—chloroplasts and photosynthesis">{{cite book |last1=Alberts |first1=Bruce |last2=Johnson |first2=Alexander |last3=Lewis |first3=Julian |last4=Raff |first4=Martin |last5=Roberts |first5=Keith |last6=Walter |first6=Peter |title=Molecular Biology of the Cell |edition=4th |date=2002 |publisher=Garland Science |chapter-url=https://www.ncbi.nlm.nih.gov/books/NBK26819/ |chapter=Chloroplasts and Photosynthesis }}</ref> thus paving the way for Russian biologist [[Konstantin Mereschkowski]] to suggest in 1905 the symbiogenic origin of the plastid.<ref>{{cite journal |vauthors=Mereschkowsky C |title=Über Natur und Ursprung der Chromatophoren im Pflanzenreiche |trans-title=About the nature and origin of chromatophores in the vegetable kingdom |language=de |journal=Biol Centralbl |year=1905 |volume=25 |pages=593–604 |url=https://archive.org/details/cbarchive_51353_bernaturundursprungderchromato1881}}</ref> [[Lynn Margulis]] brought this hypothesis back to attention more than 60 years later<ref>{{cite journal | vauthors = Sagan L | title = On the origin of mitosing cells | journal = Journal of Theoretical Biology | volume = 14 | issue = 3 | pages = 255–274 | date = March 1967 | pmid = 11541392 | doi = 10.1016/0022-5193(67)90079-3 | bibcode = 1967JThBi..14..225S }}</ref> but the idea did not become fully accepted until supplementary data started to accumulate. The cyanobacterial origin of plastids is now supported by various pieces of [[Phylogenetics|phylogenetic]],<ref>{{cite journal | vauthors = Schwartz RM, Dayhoff MO | title = Origins of prokaryotes, eukaryotes, mitochondria, and chloroplasts | journal = Science | volume = 199 | issue = 4327 | pages = 395–403 | date = January 1978 | pmid = 202030 | doi = 10.1126/science.202030 | bibcode = 1978Sci...199..395S }}</ref><ref name="Rodríguez-Ezpeleta N 2005"/><ref name="Ponce-Toledo RI 2016"/> [[Genomics|genomic]],<ref>{{cite journal | vauthors = Archibald JM | title = Genomic perspectives on the birth and spread of plastids | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 112 | issue = 33 | pages = 10147–10153 | date = August 2015 | pmid = 25902528 | pmc = 4547232 | doi = 10.1073/pnas.1421374112 | doi-access = free | bibcode = 2015PNAS..11210147A }}</ref> biochemical<ref>{{cite journal | vauthors = Blankenship RE | title = Early evolution of photosynthesis | journal = Plant Physiology | volume = 154 | issue = 2 | pages = 434–438 | date = October 2010 | pmid = 20921158 | pmc = 2949000 | doi = 10.1104/pp.110.161687 }}</ref><ref>{{cite journal | vauthors = Rockwell NC, Lagarias JC, Bhattacharya D | title = Primary endosymbiosis and the evolution of light and oxygen sensing in photosynthetic eukaryotes | journal = Frontiers in Ecology and Evolution | volume = 2 | issue = 66 | year = 2014 | pmid = 25729749 | pmc = 4343542 | doi = 10.3389/fevo.2014.00066 | doi-access = free | bibcode = 2014FrEEv...2...66R }}</ref> and structural evidence.<ref>Summarised in {{cite journal | vauthors = Cavalier-Smith T | title = Membrane heredity and early chloroplast evolution | journal = Trends in Plant Science | volume = 5 | issue = 4 | pages = 174–182 | date = April 2000 | pmid = 10740299 | doi = 10.1016/S1360-1385(00)01598-3 }}</ref> The description of another independent and more recent primary endosymbiosis event between a cyanobacterium and a separate eukaryote lineage (the [[rhizaria]]n ''[[Paulinella]] chromatophora'') also gives credibility to the endosymbiotic origin of the plastids.<ref>{{cite journal | vauthors = Nowack EC, Melkonian M, Glöckner G | title = Chromatophore genome sequence of Paulinella sheds light on acquisition of photosynthesis by eukaryotes | journal = Current Biology | volume = 18 | issue = 6 | pages = 410–418 | date = March 2008 | pmid = 18356055 | doi = 10.1016/j.cub.2008.02.051 | doi-access = free | bibcode = 2008CBio...18..410N }}</ref>

{{multiple image |total_width=450|caption_align = center
|image1=Glaucocystis sp.jpg |caption1=The chloroplasts of [[glaucophyte]]s have a [[peptidoglycan]] layer, evidence suggesting their endosymbiotic origin from cyanobacteria.<ref name="keeling">{{cite journal | vauthors = Keeling PJ | title = Diversity and evolutionary history of plastids and their hosts | journal = American Journal of Botany | volume = 91 | issue = 10 | pages = 1481–1493 | date = October 2004 | pmid = 21652304 | doi = 10.3732/ajb.91.10.1481 | doi-access = free | bibcode = 2004AmJB...91.1481K }}</ref>
|image2=Plagiomnium affine laminazellen.jpeg |caption2=Plant cells with visible chloroplasts (from a moss, ''[[Plagiomnium affine]]'')
}}
In addition to this primary endosymbiosis, many eukaryotic lineages have been subject to [[Secondary endosymbiosis|secondary]] or even [[tertiary endosymbiotic events]], that is the "[[Matryoshka doll|Matryoshka]]-like" engulfment by a eukaryote of another plastid-bearing eukaryote.<ref>{{cite journal | vauthors = Archibald JM | title = The puzzle of plastid evolution | journal = Current Biology | volume = 19 | issue = 2 | pages = R81–R88 | date = January 2009 | pmid = 19174147 | doi = 10.1016/j.cub.2008.11.067 | doi-access = free | bibcode = 2009CBio...19..R81A }}</ref><ref name="ReferenceA"/>

[[Chloroplast]]s have many similarities with cyanobacteria, including a circular [[chromosome]], prokaryotic-type [[ribosome]]s, and similar proteins in the photosynthetic reaction center.<ref>{{cite journal | vauthors = Douglas SE | title = Plastid evolution: origins, diversity, trends | journal = Current Opinion in Genetics & Development | volume = 8 | issue = 6 | pages = 655–661 | date = December 1998 | pmid = 9914199 | doi = 10.1016/S0959-437X(98)80033-6 }}</ref><ref>{{cite journal | vauthors = Reyes-Prieto A, Weber AP, Bhattacharya D | title = The origin and establishment of the plastid in algae and plants | journal = Annual Review of Genetics | volume = 41 | pages = 147–168 | year = 2007 | issue = 1 | pmid = 17600460 | doi = 10.1146/annurev.genet.41.110306.130134 }}</ref> The [[endosymbiotic theory]] suggests that photosynthetic bacteria were acquired (by [[endocytosis]]) by early [[Eukaryote|eukaryotic]] cells to form the first [[plant]] cells. Therefore, chloroplasts may be photosynthetic bacteria that adapted to life inside plant cells. Like [[mitochondrion|mitochondria]], chloroplasts still possess their own DNA, separate from the [[nuclear DNA]] of their plant host cells and the genes in this chloroplast DNA resemble those in cyanobacteria.<ref>{{cite journal | vauthors = Raven JA, Allen JF | title = Genomics and chloroplast evolution: what did cyanobacteria do for plants? | journal = Genome Biology | volume = 4 | issue = 3 | pages = 209 | year = 2003 | pmid = 12620099 | pmc = 153454 | doi = 10.1186/gb-2003-4-3-209 | doi-access = free }}</ref> DNA in chloroplasts codes for [[redox]] proteins such as photosynthetic reaction centers. The [[CoRR hypothesis]] proposes this co-location is required for redox regulation.